1. Field of the Invention
The present invention relates to an image display apparatus and method that can enhance the visual contrast of a display video image.
2. Related Art
In recent years, an image display apparatus, which is exemplified by a liquid-crystal display device, provided with a light source and a light modulation device that modulates light from the light source has widely spread. However, in such an image display apparatus as described above, the light modulation device does not have an ideal modulation characteristic; therefore, especially when a black image is displayed, light leakage from the light modulation device causes deterioration in the contrast of the displayed image.
In order to suppress the deterioration in the contrast, a plurality of methods, in which the luminance of the light source is modulated according to an input video image, has been proposed. For example, according to JP-A2005-148709 (Kokai), the modal value or the average value of gray-scale levels of an input video image is obtained, and based on the modal value or the average value, the luminance of the light source is controlled. Additionally, according to Japanese Patent No. 3583124, the peak value or the average value of gray-scale levels of an input video image is obtained, and based on the peak value and the average value, the luminance of the light source is controlled. Additionally, according to Japanese Patent No. 3495362, the average value of gray-scale levels of an input video image is obtained, and based on the average value, the luminance of the light source is controlled.
By controlling the light-source luminance in accordance with an input video image, all the foregoing techniques can enhance the contrast, compared with an image display apparatus having a constant light-source luminance. All the foregoing techniques control the light-source luminance, based on a representative value such as the average value, the modal value, or the peak value of the gray-scale levels of an input video image. However, a great number of video images exist in which, even though the foregoing representative values are the same, the respective distributions of the gray-scale levels differ from one another; In each of the foregoing techniques, the same light-source luminance is set for all the video images; therefore, in some cases, the contrast in an input video image cannot sufficiently be obtained.